Electric machine

Abstract

Method for stopping an electric machine (1), wherein - the electric machine (1) is regulated or controlled such that an output of the electric machine is essentially at rest, - if, while the output is essentially at rest, a torque and / or a force acts on the output, the torque and / or force is at least partially - preferably essentially completely - reduced by means of a regulated or controlled relief movement (E) and - the electric machine (1) is switched off without torque.

Description

The present invention relates to a method for stopping an electric machine and to an electric machine. A standard method known in the prior art for stopping an electric machine involves controlling or regulating the electric machine so that an output of the electric machine is essentially at rest, optionally activating a brake, and releasing the torque of the electric machine. The brake is intended to prevent unwanted movements of the driven device or the electric machine itself after the torque is released. However, in some specific applications, this solution is very difficult or only implementable with considerable effort. For example, electric motors are often used in injection molding machines to exert large forces. These forces cause deformations in the injection molding machine. For instance, in the clamping units of injection molding machines, the clamping force can cause elongation of tie bars or deformation of a machine frame. Significant deformations also occur in injection molds and the fixed mounting plate of injection molding machines. These are caused by the pressure of the injection unit and the pressure of the injected melt. The high counter-torques or counter-forces that occur in these applications, caused by the reversal of the aforementioned deformations and which act back on the output, cannot be compensated for by brakes. German patent application DE 102 22 539 A1 discloses a method for operating an actuator in which a DC motor is supplied with DC current via a power supply line, which can be returned to the power supply line via another line. If the power supply to the DC motor is interrupted, the rotational movement of the drive shaft is reversed by the applied torque, whereby DC current is returned by the generator voltage and the opposing torque slows down the drive shaft. The object of the invention is to provide a method for stopping an electric machine and an electric machine which allows for a less complex stopping process compared to the prior art, even in the presence of significant opposing torques and / or opposing forces. With regard to the method, this problem is solved by the features of claim 1. With regard to the electrical machine, the problem is solved by the features of claim 11. This is achieved by regulating or controlling the electric machine in such a way that an output of the electric machine is essentially at rest, if, while the output is essentially at rest, a torque and / or force acts on the output, the torque and / or force is at least partially - preferably essentially completely - reduced by means of a controlled or regulated relief movement and the electric machine is switched to torque-free operation. Since no subsequent movements occur when releasing the torque according to this method, corresponding safety brakes can be dimensioned much smaller or omitted entirely. Preferred embodiments of the invention are defined in the dependent claims. For the sake of simplicity, it may be preferable to measure the torque and / or force acting on the output while the output is essentially at rest at the electric machine. A current or torque signal from a drive controller of the electric machine can be used for this purpose, which the drive controller itself often uses for control. The torque and / or force acting on the output shaft while it is essentially at rest can also be measured externally with respect to the electric machine. Therefore, other sensors that are not part of the electric machine can also be used. For example, a clamping force sensor could be used in the clamping unit of a forming machine. To ensure a rapid and safe reduction of the torque and / or force acting on the output, it may be possible to measure a residual torque and / or force during the unloading movement. For the sake of simplicity, the residual torque and / or residual force can also be measured on the electric machine or externally. The unloading movement can be stopped as soon as the residual torque or force essentially disappears. A lower limit can be used as a criterion for both the complete reduction of the torque and / or force acting on the output, or for the disappearance of the residual torque and / or force. If this limit is not reached, the torque and / or force, or the residual torque and / or force, can be considered to be essentially reduced or eliminated. To guarantee that no coasting motion occurs, it may be preferable to regulate or control the unloading movement depending on the residual torque and / or residual force. The present invention can, in principle, be used in any electrical machine. However, its use in forming machines, particularly their clamping units and injection units, is preferred. Forming machines can be understood to include injection molding machines, injection presses, presses, and the like. The electrical machines according to the invention can preferably be provided for driving a movable mold mounting plate, an ejector, an injection unit, a plasticizing screw and / or an injection piston. Particularly advantageous is its use in connection with spring-loaded forming tools, since the loading of the springs during operation increases the likelihood of large movements after the drives are stopped – if carried out according to a prior art method. Further advantages and details of the invention are evident from the figures and the accompanying figure descriptions. Figures 1 and 2 show diagrams illustrating the prior art method and clarifying the problem statement; Figure 3 shows two diagrams illustrating the method according to the invention; Figure 4 shows a clamping unit according to the invention for an injection molding machine in a C-frame configuration; and Figure 5 shows a clamping unit according to the invention for an injection molding machine in a configuration with four tie bars. Fig. 1 shows two diagrams, the upper diagram representing the velocity V and the lower diagram the torque M, which are present or applied to the output of an electric machine 1 when it is stopped. During period I, the electric machine is initially in steady-state operation at a constant velocity V, which is maintained by a constant torque M (while performing work). At the transition from period I to period II, the electric machine 1 is stopped. The electric machine 1 is regulated or controlled so that the velocity V drops to essentially zero. For this purpose, the torque M supplied by the electric machine 1 is reversed in the direction of action. As soon as the velocity V essentially disappears within the limits of measurement accuracy, the torque M supplied by the electric machine 1 will also essentially disappear.After the speed V of the output has been regulated or controlled to essentially zero for some time, the electric machine 1 is switched to torque-free operation (during the transition from period II to period III). The ideal situation shown in Fig. 1 is characterized by the fact that there is no feedback from the device driven by the electric machine 1 to the electric machine 1 itself. The situation with a corresponding feedback effect in the form of a back EMF is shown in Fig. 2. As soon as the velocity V of the output (in time domain II) has decreased to essentially zero, the drive must continue to maintain a torque M, since the back EMF would otherwise cause movement of the output. This is precisely what happens during the transition to time domain III when the electric machine 1 is switched off without torque. The corresponding coasting motion A (also marked with a lightning symbol) is caused by the back EMF. As soon as the back EMF is reduced, the coasting motion A subsides (due to friction and the like). The critical point here is that the coasting motion A is neither regulated nor controlled, but completely uncontrolled. Therefore, it poses a safety risk. Analogous diagrams for carrying out a method according to the invention are shown in Fig. 3, in addition to those shown in Figs. 1 and 2. After the speed V of the output has been reduced to zero by regulation or control, the back E torque MR is measured. If this torque is significantly different from zero (for example, characterized by exceeding a limit value), a regulated or controlled relief movement E is performed, reducing the back E torque MR. The relief movement E is regulated or controlled such that the resulting residual torque MRest is reduced under monitoring. In this embodiment, the relief movement E is regulated according to the speed of the output of the electric machine 1, specifically as a function of the residual torque MRest. Only after both the velocity V and the torque M of the output have essentially vanished is the torque release of the electric machine 1 activated (transition to period III). Here, too, the criterion for vanishing can be the falling below certain limit values. These limit values ​​can be chosen so that the friction occurring in the system prevents movements that would be caused by the velocity V and / or the torque M not vanishing exactly. In this embodiment, the torque release is implemented from the safety circuit of the forming machine in accordance with the "Safe Torque Off Stop Category 0" of EN 60204-1. This is activated, for example, when an emergency stop is triggered (within a specified delay time) or when a protective cover is opened. If a safety-related shutdown is not necessary, an internal shutdown of the target torque at the drive controller or a shutdown of the drive controller can simply be carried out. Fig. 4 shows a clamping unit 2 of an injection molding machine, which has two electric machines 1 according to the invention. The electric machine 1 located slightly further to the left in the figure serves to drive the movable mold mounting plate 5. Two halves of an injection mold 8 are mounted on the movable mounting plate 5 and on the fixed mounting plate 7, respectively. The electric machine 1 exerts a high clamping force, which is so strong that a significant change in the distance D1 occurs due to deformation of the machine frame 10. If, in this situation, a stop signal for the corresponding electric machine 1 is received at the interface 4 of the control unit 3 of the electric machine 1 – triggered by an operator or by an internal or external error signal – the control unit 3 controls the electric machine 1 according to the invention.If this were not the case, the return movement of the machine frame 10 would trigger an uncontrolled movement of the rotor of the electric machine 1 and – more importantly – an uncontrolled movement of the mechanism 11 of the clamping unit. A similar situation applies to the centrally located electric machine 1 for driving the ejector mechanism 6. If, for example, ejection is not yet possible even though the corresponding electric machine 1 has already been activated, a change in the length of the distance D2 occurs. Here, too, an uncontrolled movement of the ejector mechanism 6 would result if the electric machine 1 were not controlled or regulated by the control device 3 according to the invention. Fig. 5 shows a figure analogous to Fig. 4, except that instead of a clamping unit 2 with a C-frame, a clamping unit 2 with four tie bars 12 is shown. Here, too, an electric motor 1 (on the left in the figure) is used to move the movable mold mounting plate 5 – in this case by means of a toggle lever mechanism 13. The second electric motor 1 is used to drive the ejector mechanism 6. Here, distance D3 is equivalent to distance D1, and distance D4 is equivalent to distance D2. Fig. 5 is intended to illustrate that the invention is not dependent on the type of injection molding machine. With any molding machine, unwanted or uncontrolled movements can be avoided when the electric motors 1 are stopped.

Claims

Method for stopping an electric machine (1), wherein - the electric machine (1) is regulated or controlled such that an output of the electric machine is essentially at rest, - if, while the output is essentially at rest, a torque and / or a force acts on the output, the torque and / or force is at least partially - preferably essentially completely - reduced by means of a regulated or controlled relief movement (E) and - the electric machine (1) is switched off without torque. Method according to claim 1, characterized in that the unloading movement (E) is carried out by means of the electric machine (1). Method according to claim 1 or 2, characterized in that the unloading movement (E) is controlled or regulated according to a speed - preferably of the output. Method according to one of claims 1 to 3, characterized in that the torque and / or force which acts on the output while the output is essentially at rest is measured at the electric machine (1). Method according to one of claims 1 to 4, characterized in that a residual torque and / or a residual force is measured during the unloading movement - preferably on the electric machine (1). Method according to claim 5, characterized in that the relief movement (E) is regulated or controlled depending on the residual torque and / or the residual force. Method according to claim 5 or 6, characterized in that the unloading movement (E) is terminated when the residual torque and / or the residual force substantially disappears. Method according to one of claims 1 to 7, characterized in that the electric machine (1) is controlled according to a speed and / or a position - in particular according to a speed and / or a position of the output. Method for operating an electric machine, wherein a method according to one of claims 1 to 8 is carried out in response to a signal from an operator and / or to an internal and / or external fault signal. Method for operating a clamping unit (2) and / or an injection unit of a forming machine with at least one electric machine (1) which is operated by means of a method according to claim 9. An electric machine comprising: an output, a measuring device for measuring a force and / or a torque acting on the output, and a control or regulating unit (3) connected to the measuring device, which has an interface (4) for transmitting a signal to trigger a shutdown of the electric machine (1), characterized in that the control or regulating unit (3) controls or regulates the electric machine (1) when a signal to trigger a shutdown is present such that: the output of the electric machine is essentially at rest; and if measuring signals from the measuring device indicate that a torque and / or a force acts on the output while the output is essentially at rest, the torque and / or the force is reduced by means of a regulated or controlled unloading movement (E).and that the control unit (3) switches the electric machine without torque after the unloading movement (E). Clamping unit and / or injection unit of a molding machine with an electric machine according to claim 11, wherein the electric machine (1) is provided in particular for driving a movable mold mounting plate (5) and / or an ejector (6) and / or the injection unit and / or a plasticizing screw and / or an injection piston.

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